Polyester-based resins, such as those formed from saturated and unsaturated polyesters, are utilized in a variety of end-use applications. The resins can be used, for example, in conjunction with other types of materials to form composites such as pre-pregs. The polyesters may also be used as sheet molding compounding (SMC) resins, casting resins, ultraviolet (UV)-cured resins, pultrusion resins, powder coatings, toner resins, corrosion resistant resins, gel coats, laminating resins, filament winding, hand lay-up, and resin transfer molding.
Traditional polyester forming resins have typically involved the reaction of polyfunctional organic acids and alcohols, more particularly, dicarboxylic acids and diols. Examples of these polyester forming processes are proposed in U.S. Pat. Nos. 3,787,526; 4,588,668, and 4,933,252. These processes, however, are disadvantageous in that long reaction times are often required. Moreover, high pressure conditions are typically needed in order for the reaction to proceed to an acceptable product yield.
A possible alternative polyester forming process involves the use of organic carbonates as set forth in U.S. Pat. No. 5,714,568. Employing carbonates is potentially more desirable than using organic acids and alcohols in preparing polyesters. In particular, utilizing carbonates involves producing carbon dioxide as a by-product which is typically easily removed from the reaction medium. In contrast, a traditional reaction between an organic acid and an alcohol yields water as a by-product. This is usually undesirable since more energy is typically required to make the reaction proceed. Moreover, it is often difficult to separate the water from the reaction medium.
Notwithstanding the above, there remains a need in the art for polyester processes involving carbonates that proceed at faster reaction rates. In particular, it would be especially desirable to enhance the solubility of the carbonate in the reaction medium in order to increase the interaction between active substituents on the reactants.
In view of the above, it is an object of the invention to provide processes for preparing polyesters utilizing organic carbonates that progress at faster reaction rates relative to conventional processes.